The electrophysiological, light microscopic and electron microscopic properties of individual neurons are to be studied in the lateral nucleus (LGN) of Macaca monkeys. Single unit, extracellular recordings will identify physiological features of each neuron prior to intracellular injections of horseradish peroxidase using iontophoresis techniques. The brain will be processed for light and electron microscopy and individually injected neurons will be analyzed to determine their morphologies. Comparison will be made between the electrophysiological, light and electron microscopic characteristics for each neuron. Emphasis will be placed on their synaptic connections. Orthograde horseradish and immunocytochemical techniques will also be used to identify non-retinal/non-cortica synaptic connections in the LGN. The results of these studies should lead to a detailed analysis of the circuitry of thr LGN, to correlations between structure and function, and to a better understanding of the normal processing of visual information at the thalamic level. Such studies should ultimately help to prevent or correct central nervous system malfunctions connected with such diseases as amblyopia and strabismus.